Research shows solar walls effective in large buildings

Reduce heat costs by 20 percent

Thermal walls effective, Minnesota State Mankato research shows.

Solar thermal walls that heat ventilation air can reduce energy consumption in large Minnesota buildings by up to 20 percent, according to a new study by three Minnesota State University, Mankato researchers.

The heat-collecting walls can save thousands of dollars per year in natural gas and electric heating costs for Minnesota commercial businesses, manufacturers, nonprofits and government agencies, according to the researchers – Patrick Tebbe, Louis Schwartzkopf and Saeed Moaveni.

Tebbe, director of the research project, is a professor of mechanical engineering at Minnesota State Mankato. Schwartzkopf is professor emeritus of physics. Moaveni, former professor of mechanical engineering at Minnesota State Mankato, is dean of engineering at Norwich University, Northfield, Vermont.

Engineering and physics students assisted with the data-gathering and analysis.

The solar thermal wall study is intended to help building operators accurately estimate potential savings from the installation of solar walls. The work was supported by the Minnesota Department of Commerce’s Office of Energy Security.

“Using solar energy to heat ventilation air means that managers of large buildings can use less fossil fuel and reduce greenhouse gas emissions,” Schwartzkopf said. “And the savings can be substantial. Payback times can be from one to eight years.”

The three-year research project collected detailed data on solar walls in three Twin Cities buildings with large ventilation requirements (a school, a police station and a manufacturing facility/corporate headquarters).

The solar walls – called “unglazed transpired solar collectors” – are dark-colored aluminum or steel collector plates perforated with tiny holes and mounted to south-facing walls. The sun heats the metal surface, and the metal’s heat energy transfers to thin layers of air on both sides of the panel. Fans pull the warmed air through the panel’s tiny perforations, and the heated air is channeled through ductwork and into the building.

The walls reduced energy consumption in the test buildings by 9 percent to 20 percent a year. One facility saved $2,400 in natural gas costs in one year, and larger facilities could save even more, the researchers concluded.

Monthly efficiencies of the solar thermal walls were typically 40-50 percent during winter months when they were most needed, with maximum efficiencies of 75 percent.